Immunosuppression is an important clinical approach in treating autoimmune disease and in preventing organ and tissue rejection. The clinically available immunosuppressants, including azathioprine, cyclosporine and tacrolimus, although effective, often cause undesirable side effects including nephrotoxicity, hypertension, gastrointestinal disturbances and gum inflammation. Inhibitors of the tyrosine kinase Jak3 are known to be useful as immunosuppressants (see U.S. Pat. No. 6,313,129).
The members of the Janus kinase (Jak) family of non-receptor intracellular tyrosine kinases are components of cytokine signal transduction. Four family members have been identified to date: Jak1, Jak2, Jak3 and Tyk2. The Jaks play a key role in the intracellular signaling mediated through cytokine receptors. Upon binding of cytokines to their receptors, Jaks are activated and phosphorylate the receptors, creating docking sites for other signaling molecules, in particular members of the signal transducer and activator of transcription (STAT) family. While expression of Jak1, Jak2 and Tyk2 is relatively ubiquitous, Jak3 expression is temporally and spatially regulated. Jak3 is predominantly expressed in cells of hematopoietic lineage; it is constitutively expressed in natural killer (NK) cells and thymocytes and is inducible in T cells, B cells and myeloid cells (reviewed in Ortmann, et al., 1999 and Yamaoka, et al., 2004). Jak3 is also is expressed in mast cells, and its enzymatic activity is enhanced by IgE receptor/FcεRI cross-linking (Malaviya and Uckun, 1999).
A specific, orally active Jak3 inhibitor, CP-690,550, has been shown to act as an effective immunosuppressant and prolong animal survival in a murine model of heart transplantation and a primate model of kidney transplantation (Changelian, et al., 2003).
Furthermore, aberrant Jak3 activity has been linked to a leukemic form of cutaneous T-cell lymphoma (Sezary's syndrome) and acute lymphoblastic leukemia (ALL), the most common form of childhood cancer. The identification of Jak3 inhibitors has provided the basis for new clinical approaches in treating leukemias and lymphomas (reviewed in Uckun, et al, 2005). Two dimethoxyquinazoline derivatives, WHI-P131 (JANEX-1) and WHI-P154 (JANEX-2), have been reported to be selective inhibitors of Jak3 in leukemia cells (Sudbeck et al., 1999).
Jak3 has also been shown to play a role in mast-cell mediated allergic reactions and inflammatory diseases and serves as a target in indications such as asthma and anaphylaxis.
Therefore, compounds that inhibit Jak3 are useful for indications such as leukemias and lymphomas, organ and bone marrow transplant rejection, mast cell-mediated allergic reactions and inflammatory diseases and disorders.